Neuropeptide Y functional amyloid aggregation reveals that self-replication can align with biological timescales

Studying amyloid fibril formation is crucial for understanding their role in neurodegenerative diseases, uncovering potential therapeutic targets, and developing interventions to mitigate their harmful effects. These fibrils can disrupt cellular functions and are implicated in various human conditions, including Alzheimer's and Parkinson's diseases. Despite their disease associations, amyloid aggregates also play multiple biological roles, including biofilm formation and regulating the release of neuropeptide into the bloodstream. The challenge lies in understanding how cells manage amyloid formation without adverse effects, as functional amyloids form on a much shorter timescale (minutes to hours) compared to disease-associated amyloids, which develop over years. This project investigates the mechanisms of Neuropeptide Y (NPY) functional amyloid aggregation, revealing significant changes in secondary structure with varying incubation times, temperatures, and chemical environments. Our findings show that NPY forms β-sheet-rich amyloids at 37 ºC and pH 5.4, conditions that mimic the secretory granule environment. Microscopy studies revealed environmentally dependent morphological variations. In heparin-free conditions, NPY assembled into dynamic oligomers that progressively organized into flexible fibrillar structures. Conversely, heparin induced the formation of rigid, well-defined fibrils with consistent diameters of ~10 nm, as confirmed by transmission electron microscopy. Kinetic analysis revealed that NPY aggregation follows a dual-pathway mechanism, combining primary nucleation with surface-catalyzed secondary nucleation. The latter dominates, driving exponential fibril growth through self-replication. Notably, NPY’s self-replication rate aligns with its functional demands, distinguishing it as a physiological amyloid where controlled aggregation is biologically essential. These findings reframe amyloids as evolutionarily optimized structures, challenging their traditional association with disease and underscoring their adaptive roles in normal cellular processes.